FIG. 12 is a perspective view showing the configuration of a crimp terminal in a related art which is similar to one described in Patent Literature 1, for example.
This crimp terminal 210 includes an electrical connecting portion 211 adapted to be connected to a terminal of a mating connector at a front portion in a longitudinal direction of the terminal (also a longitudinal direction of an electric wire to be connected thereto), additionally includes a conductor press-clamping portion 212 adapted to be crimped against a bared conductor at an end of an electric wire (whose illustration is omitted) at a portion lying rearwards of the electrical connecting portion 211 and further includes a sheath clamping portion 213 adapted to be crimped against an insulation sheath portion of the electric wire at a portion lying rearwards of the conductor press-clamping portion 212. In addition, the crimp terminal 210 includes a first connecting portion 214 lying between the electrical connecting portion 211 and the conductor press-clamping portion 212 to connect these two portions together, and a second connecting portion 215 lying between the conductor press-clamping portion 212 and the sheath clamping portion 213 to connect these two portions together.
The conductor press-clamping portion 212 is formed into a configuration having a substantially U-shaped cross section by a bottom plate 231 and a pair of conductor clamping pieces 232, 232 which extend upwards from left- and right-hand side edges of the bottom plate 231 to be crimped so as to wrap the conductor of the electric wire which is disposed on an inner surface of the bottom plate 231. In addition, the sheath clamping portion 213 is formed into a configuration having a substantially U-shaped cross section by a bottom plate 261 and a pair of sheath clamping pieces 262, 262 which extend upwards from left- and right-hand side edges of the base plate 261 to be crimped against (the insulation sheath portion of) the electric wire which is disposed on an inner surface of the bottom plate 261.
The first connecting portion 214 and the second connecting portion 215 which are formed at the front and rear of the conductor press-clamping portion 212 are both formed into configurations having a substantially U-shaped cross section by bottom plates 221, 251 and low side plates 222, 252 which are erected from left- and right-hand side edges of the bottom plates 221, 251.
Then, a bottom plate (not shown) of the electrical connecting portion 211 at a front portion and the bottom plates 221, 231, 251, 261 through the sheath clamping portion 213 at the rearmost portion are formed continuously like a single belt-shaped plate. In addition, front and rear ends of the low side plates 222 of the first connecting portion 214 connect, respectively, to lower half portions of rear ends of side plates (whose reference numerals are omitted) of the electrical connecting portion 211 and front ends of the conductor clamping pieces 232 of the conductor press-clamping portion 212. Front and rear ends of the low side plates 252 of the second connecting portion 215 connect, respectively, to lower half portions of rear ends of the conductor clamping pieces 232 of the conductor press-clamping portion 212 and front ends of the sheath clamping pieces 262 of the sheath clamping portion 213.
A plurality of recessed groove-like serrations 235, which extend in a direction which is at right angles to the longitudinal direction of the conductor of the electric wire (the longitudinal direction of the terminal), are provided on an inner surface of the conductor press-clamping portion 212.
To crimp the conductor press-clamping portion 212 of the crimp terminal 210 against the conductor at the end of the electric wire, the crimp terminal 210 is placed on a placing surface (an upper surface) of a lower mold (an anvil), not shown, and the conductor at the end of the electric wire is inserted between the conductor clamping pieces 232 of the conductor press-clamping portion 212 to thereby be placed on an upper surface of the bottom plate 231. Then, an upper mold (a crimper) is lowered relative to the lower mold to thereby bring down distal end portions of the conductor clamping pieces 232 gradually inwards by sloping guide planes of the upper mold. As this occurs, the left and right conductor clamping pieces 232 are bent to be deformed about portions lying in proximity to left and right edge portions 231a of the bottom plate 231.
Then, by lowering the upper mold (the crimper) further downwards relative to the lower mold, the distal ends of the conductor clamping pieces 232 are finally rounded in a folded back fashion by curved planes of the upper mold which connect from the sloping guide planes to a central angular portion thereof, whereby the conductor clamping pieces 232 are crimped so as to wrap the conductor Wa by causing the distal ends of the conductor clamping pieces 232 to bite into the conductor Wa while causing them to rub against each other, as is shown in (a) of FIG. 13.
By the series of operations, the conductor press-clamping portion 212 of the crimp terminal 210 can be connected to the conductor Wa of the electric wire through crimping. Also, with respect to the sheath clamping portion 213, the sheath clamping pieces 262 are bent gradually inwards by use of the upper and lower molds in a similar fashion and the sheath clamping pieces 262 are crimped against the insulation sheath portion of the electric wire. By doing this, the crimp terminal 210 can be connected to the electric wire electrically and mechanically.
Incidentally, when the crimp terminal 210 is connected to the electric wire in the way described above, the reliability of the crimped portions need to be evaluated, and to make this happen, thermal shock tests are performed from time to time.
A thermal shock test is performed to inspect a durability in severe conditions which can cover all service conditions which are considered to occur in reality. For example, in the case of crimped portions of an automotive terminal, the crimped portions are repeatedly subjected to low-temperature conditions and high-temperature conditions.
When a thermal shock test like this is performed on the crimp terminal 210, the conductor press-clamping portion 212 of the crimp terminal 210 and the conductor Wa of the electric wire expand or contract (expand or shrink). For example, assuming that a shape indicated by solid lines in (a) of FIG. 13 shows a state at ordinary temperatures, the conductor press-clamping portion 212 expands to a shape indicated by dotted lines at high temperatures.
When the rigidity of the conductor press-clamping portion 212 is sufficiently high, even in the event that the conductor press-clamping portion 212 and the conductor Wa expand or contract in accordance with a change in temperature, the conductor press-clamping portion 212 restores its original crimped shape at ordinary temperatures. However, in the case of a terminal which is made small in size or thin in thickness, the rigidity of the terminal tends to decrease, and therefore, the shape of a conductor press-clamping portion is made difficult to restore its original crimped shape after such a thermal shock test has been carried out thereon, and there may occur a case where the conductor press-clamping portion cannot restore its original crimped shape completely as is shown in (b) of FIG. 13. Namely, there may occur a case where a portion of the conductor press-clamping portion where distal ends of left and right conductor clamping pieces 232 rub against each other tends to open and cannot be restored completely to its original condition.
For example, as is indicated by the solid lines in (a) of FIG. 13, when crimped, the distal ends of the conductor clamping pieces 232 of the conductor press-clamping portion 212 bite into the conductor Wa. However, when a biting amount e1 of the distal ends of the conductor clamping pieces 232 is not so large (when a biting depth of the distal ends is shallow), a phenomenon tends to occur easily in which the conductor clamping pieces 232 do not restore their original crimped shapes completely after the thermal shock test is carried out thereon, as a result of which as is shown by a dimension e2 in (b) of FIG. 13, there may occur a situation in which the biting depth becomes shallower.
In this way, when the conductor clamping pieces 232 are made difficult to restore their original crimped shapes, whereby the portion where the distal ends of the conductor clamping portions 232 tends to open or the biting depth of the conductor clamping pieces 232 into the conductor Wa becomes shallow, the clamping of the conductor Wa by the conductor clamping pieces 232 becomes weak, whereby a contact pressure (a contact load) F to the conductor Wa exerted by the conductor clamping pieces 232 is reduced. When the contact pressure F is reduced, a securing force (a mechanical connecting force) and an electrical conductivity (an electrical connection property) at the connecting portion between the crimp terminal 210 and the electric wire are reduced.
On the other hand, in recent years, to reduce the weight of a wiring harness, the replacement of copper electric wires with aluminum electric wires is now studied, and actually, there are many cases where a copper terminal is connected to an aluminum electric wire. However, it has been found that in such a case, due to there being a difference in thermal expansion between the crimp terminal and the conductor, the contact pressure between the crimp terminal and the conductor tends to be reduced further.